Eric Rawlins has created a website listing leitmotifs in the Lord of the Rings film scores. First I have to point out the excellent advice he gives on labeling and interpreting these motives. As has been pointed out by countless philosophers, musicians, and cognitive scientists, music has the ability to express what cannot be expressed by words. These leitmotifs are an example of that. The concepts change as the context, harmonic underpinning, or melodic overpinning(?) is altered. Likewise, the melding of music with visual elements can create new complex associations (e.g. the use of Barber's Adagio in Platoon.) Eric focuses on the latter much more than the former, and keeps all musical analysis to a novice level.
Second, I have to point to one motif that I think Eric mislabels/misinterprets. The Ring motif is indeed used quite often when the Ring is mentioned. But it also occurs at the Argonath scene, as Eric rightly points out, and when Galadriel mentions how things have been lost and forgotten in the prelude of the first film. While the motif does represent the Ring, it also represents all the lost lore/wisdom/culture of the previous ages. Man can no longer build things like the Argonath. The end of the Ring means the end of the Elves power and culture. I think it overall represents the transition from the Elf-dominated world to a new one, which will be dominated by either Men or Orcs. It also captures the tone of Tolkein's books, with a nostalgic focus on the glories of the past, never to be repeated.
I'm thinking of teaching a course on the music of the Lord of the Rings for Winter Term in two years. It would include the film scores, with the extended DVD documentaries, score reviews (including Jaquandar's), and this site. It would also look at LOTR-inspired music, from band music to rock and jazz. I think it would be a good way to sneak in some basics of semiotics, while making for a fun course.